1. Field of Invention
The present invention relates to a mold for a drum-shaped magnetic core which is used for small inductor parts in various kind of electric appliances.
2. Description of Related Art
Generally, a drum-shaped of magnetic core is obtained by forming the general shape by compressing magnetic powder. Various grinding, horizontal compression molding, and individual compression molding and subsequent bonding processes have been used. These processes are explained below.
In a grinding process, using a powder-compressing press, the magnetic powder is formed into a round pole-like shape having a specific diameter as shown in FIG. 12. Then, and as shown in FIG. 13, the sides of the round pole-like shape are reduced using a grinding stone to form a drum-shaped magnetic core. As shown in FIG. 14, the resulting drum-shaped magnetic core has an upper flange la and a lower flange 1b connected by a winding core portion 2.
In the horizontal compression molding process, as shown in FIG. 15, a mold is provided having a cavity shaped to mold a drum-shaped winding core portion 2, in a horizontal posture. Magnetic powder is filled and compressed to make a drum-shaped of magnetic core in one process (lateral pushing method). However, the horizontal compression molding process, as shown in FIG. 16, produces a cut portion 1c on the upper flange 1a, a cut portion 1d on the lower flange 1b and a cut portion 2a on the winding core portion 2.
In the individual compression molding and subsequent bonding processes method, as shown in FIG. 17, the upper flange 1a, the lower flange 1b and the winding core portion 2 are individually formed by powder compression molding. These separately formed members are subsequently bonded together using adhesives to obtain the same structure as shown in FIG. 14.
However, the above conventional methods include the following problems respectively. First, in the case of the grinding processes, because a molded pole-like shape must be formed first, an increased volume of magnetic powder must be used. Furthermore, because the sides of the molded pole-like shape must be reduced to produce the winding core portion, numerous cutting chips are generated. These cutting chips may contaminate the manufacturing environment. Thus, economical efficiency is reduced by this method.
In the horizontal compression molding process, as shown in FIG. 15 and discussed above, cut portions 1c, 1d and 2a are produced. These cut portions result in a winding core portion 2 with a reduced sectional area when compared with a pole having the same diameter that does not have such a cut portion. Thus, the cut portion of the winding core portion 2 must be supplemented to increase the sectional area of the winding core portion 2. However, an increase in the sectional area of the winding core portion 2 causes a decrease in the number of windings that can be accommodated on the winding core portion 2. Thus, the overall function of the drum-shaped of magnetic core is reduced. In order to avoid this problem, various limitations on the dimensions of each portion of the drum-shaped of magnetic core must be considered.
Furthermore, burs are generated on the ends of the cut portions 1c, 1d and 2a. Accordingly a bur-removing process must be performed. This merely increases the number of processes steps required in the horizontal compression molding process.
Therefore, although the desired drum-shaped core can be molded using the horizontal compression molding process, an reduction in production cost could not be expected. Moreover, is impossible to arrange a horizontal compression mold to produce a drum-shaped of magnetic core having all of the various shapes of flanges illustrated in FIG. 9(a)-(d).
In the individual compression molding and subsequent bonding processes method, as shown in FIG. 17 and described above, the bonding process for each member is inevitable. The bonding process causes an increased number of processes steps and cost. Furthermore, the individual compression molding and subsequent bonding processes method results in bonded members that are easily separated due to poor bonding.